public void First_non_repeating_letter_Test(string Input, string Output)
{
var res = Task2.First_non_repeating_letter(Input);
Assert.AreEqual(res, Output);
}
public void First_non_repeating_letter_Test(string input_str, char output_char)
{
var res = Task2.First_non_repeating_letter(input_str);
Assert.AreEqual(res, output_char);
}